Tuning to a correct frequency at reception is important to achieve a proper wireless reception. In the case of a terminal which receives a transmission, e.g. from a base station, there can be several reasons for frequency to be corrected: drift in a reference oscillator of the terminal, Doppler effects, difference in frequency alignment for different transmitters performing the transmission, etc. To be able to correct the frequency, often referred to as ‘tuning’, a proper frequency offset need to be available. Here, the frequency offset is a discrepancy between an expected or preset frequency and the actual frequency on which the transmission relies.
European patent application published as EP 1 988 676 A1 discloses an analytical approach for determining a frequency error in a receiver of a wireless system. In particular, EP 1 988 676 A1 discloses an approach for an Orthogonal Frequency Division Multiplex (OFDM) receiver, where symbols of a given duration are transmitted as cells on sub-carrier frequencies where some of the cells are pilot cells modulated with reference information. The approach comprises selection of at least three pilot cells from different symbols and different sub-carriers, as illustrated by example of FIG. 1. The symbol and the sub-carrier on which each pilot cell is transmitted are determined. For each pilot cell, a phase difference is determined between received and generated signals. From that, a change in phase difference is calculated, from which the frequency error in turn is calculated. A particular advantage of this is that frequency error can be calculated from even short transmissions, such as a single resource block. A further advantage is that by selecting a multitude of pilot cells, the calculation can result in a very precise result.
However, although the result can be very precise, there are further qualities of determination of a frequency error that can be appreciated. One of them can be low demand on processing power; another can be real-time properties. The inventors have identified a further quality issue that needs to be addressed: robustness of the frequency offset estimation. The present invention is therefore inclined towards an improvement regarding this issue.